Method of fabricating contact structure

1. A method of fabricating a contact structure, comprising: forming an opening in a dielectric layer; forming a conductive material layer within the opening and on the dielectric layer, wherein the conductive material layer comprises a bottom section having a first thickness and a top section having a second thickness, the second thickness is greater than the first thickness; performing a first treatment on the conductive material layer to form a first oxide layer on the bottom section and on the top section of the conductive material layer; and performing a second treatment to remove at least portions of the first oxide layer and at least portions of the conductive material layer, wherein after performing the second treatment, the bottom section and the top section of the conductive material layer have substantially equal thickness.

2. The method according to claim 1, wherein the first treatment comprises a conformal oxide treatment to form the first oxide layer conformally on the bottom section and on the top section of the conductive material layer.

3. The method according to claim 2, wherein the second treatment comprises: a first etching process that selectively removes the first oxide layer to reveal the top section of the conductive material layer, while the first oxide layer on the bottom section is retained, and a second etching process that removes parts of the top section of the conductive material layer, and removes the first oxide layer on the bottom section, wherein the second etching process has a higher etching selectivity for a conductive material of the conductive material layer than the first oxide layer.

4. The method according to claim 1, wherein the first treatment comprises a gradient oxide treatment that selectively form the first oxide layer on the conductive material layer with a thickness that decreases from the top section to the bottom section.

5. The method according to claim 4, wherein the second treatment comprises an etching process that removes the first oxide layer on the top section and the bottom section of the conductive material layer, and further removes parts of the bottom section of the conductive material layer, and wherein the etching process has a higher etching selectivity for the first oxide layer than a conductive material of the conductive material layer.

6. The method according to claim 1, further comprising repeating the first treatment and the second treatment a plurality of times until the top section of the conductive material layer is completely removed, and a portion of the bottom section of the conductive material layer is retained.

7. The method according to claim 1, further comprising forming a conductive contact filling up the opening of the dielectric layer.

8. A method, comprising: providing a substrate have a semiconductor region; forming a dielectric layer on the substrate, and patterning the dielectric layer to form an opening revealing the semiconductor region; forming a first metal layer along a top surface of the dielectric layer and along sidewalls and a bottom surface of the opening, wherein the first metal layer has an overhang portion; performing an oxide treatment on the first metal layer to form a metal oxide of the first metal layer along a surface of the first metal layer and on the overhang portion; performing an etching process to remove the metal oxide and the overhang portion of the first metal layer; removing the first metal layer on the top surface of the dielectric layer and on the sidewalls of the opening, while retaining a portion of the first metal layer on the bottom surface of the opening; and forming a second metal layer in the opening over the portion of the first metal layer.

9. The method according to claim 8, further comprising forming a liner layer in the opening prior to forming the first metal layer, and forming the first metal layer on the liner layer.

10. The method according to claim 8, wherein the etching process comprises a dry etching step for removing the metal oxide on the overhang portion, and a wet etching step for removing the overhang portion.

11. The method according to claim 8, wherein the etching process comprises a dry etching step or a wet etching step for removing the metal oxide along with the overhang portion.

12. The method according to claim 11, wherein the dry etching step comprises using WCl5 for dry etching, and the wet etching step comprises using NH4OH for wet etching.

13. The method according to claim 8, wherein the oxide treatment comprises O2 plasma treatment with an oxygen flow of 5 sccm to 20 sccm, a processing time of 20 seconds or less, and a processing temperature of 300° C. to 550° C.

14. The method according to claim 8, wherein the first metal layer is tungsten, and the metal oxide is tungsten oxide.

15. The method according to claim 8, wherein after performing the etching process to remove the metal oxide and the overhang portion of the first metal layer, an anti-reflective coating is formed to partially cover the first metal layer, and wherein the first metal layer on the top surface of the dielectric layer and on the sidewalls of the opening not covered by the anti-reflective coating are removed.